There are numerous instances where a worker is forced to work in a less than pleasant atmosphere while he is performing a demanding task. Often, the atmosphere is not only contaminated with particulate matter, either solid or liquid, but also uncomfortably hot, in the range from 80.degree. F. to 110.degree. F. A welder in a welding room, a painter in a paint booth, a construction worker on a hot dusty dam-site, a coal miner in a coal mine, are examples of workers routinely subjected to heat and contaminated air. To ameliorate such a worker's condition, any improvement of his personal comfort, even if only a small enhancement, is greatly appreciated. In addition, breathing cooled (and correspondingly dehumidified) filtered air is more conducive to his health than breathing ambient air which is only filtered. Moreover, the use of the device of this invention by workers contributes greatly to meeting the OSHA regulations which apply to the aforementioned environments in which they work.
This invention evolved from an implementation of the concept that no matter how hot the workplace is, a very small difference in temperature, as little as 0.5.degree. C., preferably from 1.degree. C. to 4.degree. C., and a very small flow of air in the range from 3 SCFM to 15 SCFM, across the face of a worker, will make a disproportionately large improvement in the feeling of comfort; more so, if the cooled, filtered air, cooler by only such a small difference in temperature, is slowly, substantially continuously flowed downwardly across the face of a worker, first cooling the forehead. With this concept it became unnecessary to specify a discharge temperature for cooled air to be supplied to the worker's headgear, and necessary only to maintain a ratio between the intake ambient temperature and the outlet discharge temperature of the cooled air. Most importantly, in the upper portion of the critical temperature range from 27.degree. C.-43.degree. C. (80.degree. F.-110.degree. F.) where a worker experiences progressively greater discomfort, cooler air relative to the ambient, is produced than in the lower portion of the range. For example, when the ambient air is 37.8.degree. C. (100.degree. F.) the device discharges cool air at about 33.9.degree. C. (93.degree. F.) when the ambient air is 80.degree. F., the device discharges cool air at about 74.5.degree. F. Stated differently, the worker gets cooler air than ambient.
Except in the relatively recent past, no effort was made to cool the air ducted to the worker, as for example in the ventilated welding helmet disclosed in U.S. Pat. No. 3,584,314.
More recently, improvement in the personal comfort of a worker is conventionally provided by ducting cooled and filtered air from an external source, removed from the ambient atmosphere in which the worker toils, through a duct which discharges the cool filtered air over his face. In a typical situation, cool, clean air is supplied from an air-conditioned "clean room" to an air manifold within the workroom. The ends of several individual air-ducts are manifolded to the air manifold, each duct connected at its other end to headgear, typically a helmet, worn by an individual worker. Even with a long air-duct, the mobility of the worker is restricted by the length of the duct which tethers him to the manifold. Such a connection to a manifold precludes easy access of the worker to a host of different physical situations. A more serious restriction is the danger associated with dragging an air-duct around a workplace which may contain machinery in which the air-duct might be entangled. Any air duct connected to an external source entails a safety problem because it may prove to be a dangerous encumbrance for a worker working with dangerous equipment.
To avoid connecting an air-duct to a manifold, there is commercially available a fresh-air system (available from Racal Health & Safety Inc.) which provides a belt-mounted blower and battery. One or more air filters are removably disposed on the intake of the blower and the discharge is ducted through an air-duct to the top of a helmet, and thence downwardly across the face of the wearer, between the air-impermeable face mask and his face. Because air blown across the face of the worker is at ambient temperature, the cooling effect relied upon is that of a fan which circulates ambient air; and because air discharged from the fan must travel through several feet (about a meter) of air-duct, the blower must be large enough not only to blow a large volume of air, but also to overcome the pressure drop through the relatively long air-duct.
It seemed that an air-cooling and air-filtration system which could be relatively unobtrusively carried on the person of a worker should meet the need for a self-contained air-cooling and filtering system. Except that, under the circumstances, not many devices could be adapted to fill such a need.
The Peltier-effect has been used in heat pumps for heating or cooling of spaces and of materials under circumstances where a conventional fluid-refrigeration cycle is disadvantageous. Whether used to heat or cool, depends upon the polarity of the unidirectional electrical energy supplied to a thermoelectric module by conductors. When one side of the Peltier thermoelectric module used in this invention is energized, it will become hot and the other side will become cold. For the purpose of this invention, the module is arranged with the cold side in heat-conductive association with the intake of a cooling air duct. The hot side is thermally associated with ambient air so that heat from the module is discharged to the ambient air.
In a thermoelectric module ("TEM" for brevity), a cold junction is produced where heat is absorbed by electrons while moving from a lower energy state to a higher energy state. A power supply provides the energy required to move electrons through the energy state system. A heat exchanger is attached to a hot junction to expel excess heat. When the Peltier-effect is used in a heat pump, the Peltier battery or pile is associated with a heat sink or heat exchanger jacket to which the heat is promoted, the heat exchanger being provided with ribs, channels or the like to facilitate the heat transfer to or from the Peltier pile over a large surface of high thermal conductivity.
The use of such thermoelectric heat pumps is limited to situations arising out of special considerations such as size, space, weight, environmental considerations, etc. This invention provided just such a special consideration, and the commercial availability of a single TEM, small enough to be mounted within a helmet-mounted housing, yet powerful enough to supply a mass-flow of cool air to minimize the discomfort due to heat and humidity, of a worker who is required to wear headgear restricting the flow of air about his face, especially in hot or dusty areas, spurred the utilization of such a module.